Influence of nonuniform surface potential on the measurement of plasma parameters by electrostatic probes

Abstract

In the theory of electrostatic probes, it is usually assumed that the probe surface potential is uniform. However, nonuniformity of the surface work function produces a nonuniformity in surface potential which may modify the current collection. This effect is examined for an infinite cylinder immersed in a collisionless plasma in the limit when Debye length is much greater than probe radius, by numerically following charged‐particle orbits in a Laplace potential. It is shown that only large‐scale, macroscopic potential nonuniformities are important for the current collection, and that microscopic nonuniformities are smoothed over relatively short distance by the Laplace equation character of the potential.

The OEDIPUS Experiment: Analysis of the current/voltage data

“…We examine theoretically the validity of a mathematical model; particularly, we made a distinction between a forward and a backward analysis. The results concur well with the model [Godard and Laframboise, 1983]. We were able to rebuild the difference of potential between the two payloads and the plasma, to estimate the different collected currents.…”

“…Finally,'the vehicle potential was also measured by th e particle analyzers. Since this article focuses on the response of a large probe in a magnetoplasma and on tests of the mathematical model [Godard and Laframboise, 1983], we would like to reformulate our approach in mathematical terms. We could have…”